281 research outputs found
Vortex in Maxwell-Chern-Simons models coupled to external backgrounds
We consider Maxwell-Chern-Simons models involving different non-minimal
coupling terms to a non relativistic massive scalar and further coupled to an
external uniform background charge. We study how these models can be
constrained to support static radially symmetric vortex configurations
saturating the lower bound for the energy. Models involving Zeeman-type
coupling support such vortices provided the potential has a "symmetry breaking"
form and a relation between parameters holds. In models where minimal coupling
is supplemented by magnetic and electric field dependant coupling terms, non
trivial vortex configurations minimizing the energy occur only when a non
linear potential is introduced. The corresponding vortices are studied
numericallyComment: LaTeX file, 2 figure
Galactic Spiral Structure
We describe the structure and composition of six major stellar streams in a
population of 20 574 local stars in the New Hipparcos Reduction with known
radial velocities. We find that, once fast moving stars are excluded, almost
all stars belong to one of these streams. The results of our investigation have
lead us to re-examine the hydrogen maps of the Milky Way, from which we
identify the possibility of a symmetric two-armed spiral with half the
conventionally accepted pitch angle. We describe a model of spiral arm motions
which matches the observed velocities and composition of the six major streams,
as well as the observed velocities of the Hyades and Praesepe clusters at the
extreme of the Hyades stream. We model stellar orbits as perturbed ellipses
aligned at a focus in coordinates rotating at the rate of precession of
apocentre. Stars join a spiral arm just before apocentre, follow the arm for
more than half an orbit, and leave the arm soon after pericentre. Spiral
pattern speed equals the mean rate of precession of apocentre. Spiral arms are
shown to be stable configurations of stellar orbits, up to the formation of a
bar and/or ring. Pitch angle is directly related to the distribution of orbital
eccentricities in a given spiral galaxy. We show how spiral galaxies can evolve
to form bars and rings. We show that orbits of gas clouds are stable only in
bisymmetric spirals. We conclude that spiral galaxies evolve toward grand
design two-armed spirals. We infer from the velocity distributions that the
Milky Way evolved into this form about 9 Gyrs ago.Comment: Published in Proc Roy Soc A. A high resolution version of this file
can be downloaded from http://papers.rqgravity.net/SpiralStructure.pdf. A
simplified account with animations begins at
http://rqgravity.net/SpiralStructur
Visibility diagrams and experimental stripe structure in the quantum Hall effect
We analyze various properties of the visibility diagrams that can be used in
the context of modular symmetries and confront them to some recent experimental
developments in the Quantum Hall Effect. We show that a suitable physical
interpretation of the visibility diagrams which permits one to describe
successfully the observed architecture of the Quantum Hall states gives rise
naturally to a stripe structure reproducing some of the experimental features
that have been observed in the study of the quantum fluctuations of the Hall
conductance. Furthermore, we exhibit new properties of the visibility diagrams
stemming from the structure of subgroups of the full modular group.Comment: 8 pages in plain TeX, 7 figures in a single postscript fil
3D MHD Modeling of the Gaseous Structure of the Galaxy: Synthetic Observations
We generated synthetic observations from the four-arm model presented in
Gomez & Cox (2004) for the Galactic ISM in the presence of a spiral
gravitational perturbation. We found that velocity crowding and diffusion have
a strong effect in the l-v diagram. The v-b diagram presents structures at the
expected spiral arm velocities, that can be explained by the off-the-plane
structure of the arms presented in previous papers of this series. Such
structures are observed in the Leiden/Dwingeloo HI survey. The rotation curve,
as measured from the inside of the modeled galaxy, shows similarities with the
observed one for the Milky Way Galaxy, although it has large deviations from
the smooth circular rotation corresponding to the background potential. The
magnetic field inferred from a synthetic synchrotron map shows a largely
circular structure, but with interesting deviations in the midplane due to
distortion of the field from circularity in the interarm regions.Comment: Accepted for publication in ApJ. Better quality figures in
http://www.astro.umd.edu/~gomez/publica/3d_galaxy-3.pd
Enhanced small-scale Faraday rotation in the Galactic spiral arms
We present an analysis of the rotation measures (RMs) of polarized
extragalactic point sources in the Southern Galactic Plane Survey. This work
demonstrates that the statistics of fluctuations in RM differ for the spiral
arms and the interarm regions. Structure functions of RM are flat in the spiral
arms, while they increase in the interarms. This indicates that there are no
correlated RM fluctuations in the magneto-ionized interstellar medium in the
spiral arms on scales larger than ~ 0.5 deg, corresponding to ~ 17 pc in the
nearest spiral arm probed. The non-zero slopes in interarm regions imply a much
larger scale of RM fluctuations. We conclude that fluctuations in the
magneto-ionic medium in the Milky Way spiral arms are not dominated by the
mainly supernova-driven turbulent cascade in the global ISM but are probably
due to a different source, most likely H II regions.Comment: 4 pages, 1 figure. ApJ Letters, in pres
The Southern Galactic Plane Survey: The Test Region
The Southern Galactic Plane Survey (SGPS) is a project to image the HI line
emission and 1.4 GHz continuum in the fourth quadrant of the Milky Way at high
resolution using the Australia Telescope Compact Array (ATCA) and the Parkes
Radio Telescope. In this paper we describe the survey details and goals,
present lambda 21-cm continuum data, and discuss HI absorption and emission
characteristics of the SGPS Test Region (325.5 deg < l < 333.5 deg; -0.5 deg <
b < +3.5 deg). We explore the effects of massive stars on the interstellar
medium (ISM) through a study of HI shells and the HI environments of HII
regions and supernova remnants. We find an HI shell surrounding the HII region
RCW 94 which indicates that the region is embedded in a molecular cloud. We
give lower limits for the kinematic distances to SNRs G327.4+0.4 and G330.2+1.0
of 4.3 kpc and 4.9 kpc, respectively. We find evidence of interaction with the
surrounding HI for both of these remnants. We also present images of a possible
new SNR G328.6-0.0. Additionally, we have discovered two small HI shells with
no counterparts in continuum emission.Comment: 17 pages, 7 embedded EPS figures, 10 low-res jpeg figures, uses
emulateapj5.sty. Accepted for publication in the Astrophysical Journal.
Version with all full resolution figures embedded is available at
http://www.astro.umn.edu/~naomi/sgps/papers/SGPS.ps.g
New infrared star clusters in the southern Milky Way with 2MASS
We carried out a 2MASS J, H and K_s survey of infrared star clusters in the
Milky Way sector 230 350. This zone was the
least studied in the literature, previously including only 12 infrared clusters
or stellar groups with 10, according to the recent catalogue
by Bica et al. (2003). We concentrated efforts on embedded clusters, which are
those expected in the areas of known radio and optical nebulae. The present
study provides 179 new infrared clusters and stellar groups, which are
interesting targets for detailed future infrared studies. The sample of
catalogued infrared clusters and stellar groups in the Galaxy is now increased
by 63%.Comment: 8 pages, 10 figures, accepted to A&A. Tables 3 and 4 available in
eletronic form at CD
The distance to a star forming region in the Outer arm of the Galaxy
We performed astrometric observations with the VLBA of WB89-437, an H2O maser
source in the Outer spiral arm of the Galaxy. We measure an annual parallax of
0.167 +/- 0.006 mas, corresponding to a heliocentric distance of 6.0 +/- 0.2
kpc or a Galactocentric distance of 13.4 +/- 0.2 kpc. This value for the
heliocentric distance is considerably smaller than the kinematic distance of
8.6 kpc. This confirms the presence of a faint Outer arm toward l = 135
degrees. We also measured the full space motion of the object and find a large
peculiar motion of ~20 km/s toward the Galactic center. This peculiar motion
explains the large error in the kinematic distance estimate. We also find that
WB89-437 has the same rotation speed as the LSR, providing more evidence for a
flat rotation curve and thus the presence of dark matter in the outer Galaxy.Comment: The Astrophysical Journal, accepted, 16 pages, 4 Figure
Swift-BAT Survey of Galactic Sources: Catalog and Properties of the populations
We study the populations of X-ray sources in the Milky Way in the 15-55 keV
band using a deep survey with the BAT instrument aboard the Swift observatory.
We present the logN-logS distributions of the various source types and we
analyze their variability and spectra. For the low-mass X-ray binaries (LMXBs)
and the high-mass X-ray binaries (HMXBs) we derive the luminosity functions to
a limiting luminosity of L_X~7 times10^{34} erg s/s. Our results confirm the
previously found flattening of the LMXB luminosity function below a luminosity
of L_X~10^{37} erg s/s. The luminosity function of the HMXBs is found to be
significantly flatter in the 15-55 keV band than in the 2-10 keV band. From the
luminosity functions we estimate the ratios of the hard X-ray luminosity from
HMXBs to the star-formation rate, and the LMXB luminosity to the stellar mass.
We use these to estimate the X-ray emissivity in the local universe from X-ray
binaries and show that it constitutes only a small fraction of the hard X-ray
background.Comment: 21 pages, accepted by Ap
A Study of Cyg OB2: Pointing the Way Towards Finding Our Galaxy's Super Star Clusters
New optical MK classification spectra have been obtained for 14 OB star
candidates identified by Comeron et al. (2002) and presumed to be possible
members of the Cyg OB2 cluster. All 14 candidate OB stars observed are indeed
early-type stars, strongly suggesting the remaining 31 candidates identified by
Comeron et al. are also early-type stars. However, as many as half of the new
stars appear to be significantly older than the previously studied optical
cluster, making their membership in Cyg OB2 suspect. Despite this, the
recognition of Cyg OB2 being a more massive and extensive star cluster than
previously realized, along with the recently recognized candidate super star
cluster Westerlund 1 only a few kpc away (Clark & Negueruela 2002), reminds us
that we are woefully under-informed about the massive cluster population in our
Galaxy. Extrapolations of the locally derived cluster luminosity function
indicate 10s to perhaps 100 of these very massive open clusters (Mcl ~ 10^4
M_sun, Mv ~ -11) should exist within our galaxy. Radio surveys will not detect
these massive clusters if they are more than a few million years old. Our best
hope for remedying this shortfall is through deep infrared searches and follow
up near-infrared spectroscopic observations, as was used by Comeron et al. to
locate candidate members of the Cyg OB2 association.Comment: 30 pages, 12 figures, ApJ in pres
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